Analog Devices AD7228ATQ, AD7228ACR, AD7228ACQ, AD7228ACP, AD7228ACN Datasheet

...
REV. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
a
LC2MOS
Octal 8-Bit DAC
AD7228A
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 617/329-4700 Fax: 617/326-8703
FUNCTIONAL BLOCK DIAGRAM
PRODUCT HIGHLIGHTS
1. Eight DACs and Amplifiers in Small Package The single-chip design of eight 8-bit DACs and amplifiers al­lows a dramatic reduction in board space requirements and offers increased reliability in systems using multiple convert­ers. Its pinout is aimed at optimizing board layout with all analog inputs and outputs at one side of the package and all digital inputs at the other.
2. Single or Dual Supply Operation The voltage-mode configuration of the DACs allows single supply operation of the AD7228A. The part can also be oper­ated with dual supplies giving enhanced performance for some parameters.
3. Microprocessor Compatibility The AD7228A has a common 8-bit data bus with individual DAC latches, providing a versatile control architecture for simple interface to microprocessors. All latch enable signals are level triggered and speed compatible with most high per­formance 8-bit microprocessors.
FEATURES Eight 8-Bit DACs with Output Amplifiers Operates with Single +5 V, +12 V or +15 V
or Dual Supplies
mP Compatible (95 ns
WR Pulse) No User Trims Required Skinny 24-Pin DlPs, SOIC, and 28-Terminal Surface
Mount Packages
GENERAL DESCRIPTION
The AD7228A contains eight 8-bit voltage-mode digital-to­analog converters, with output buffer amplifiers and interface logic on a single monolithic chip. No external trims are required to achieve full specified performance for the part.
Separate on-chip latches are provided for each of the eight D/A converters. Data is transferred into the data latches through a common 8-bit TTL/CMOS (5 V) compatible input port. Ad­dress inputs A0, A1 and A2 determine which latch is loaded when
WR goes low. The control logic is speed compatible with
most 8-bit microprocessors. Specified performance is guaranteed for input reference voltages
from +2 to +10 V when using dual supplies. The part is also specified for single supply +15 V operation using a reference of +10 V and single supply +5 V operation using a reference of +1.23 V. Each output buffer amplifier is capable of developing +10 V across a 2 k load.
The AD7228A is fabricated on an all ion-implanted, high­speed, Linear Compatible CMOS (LC
2
MOS) process which has been specifically developed to integrate high-speed digital logic circuits and precision analog circuits on the same chip.
REV. A
–2–
AD7228A–SPECIFICA TIONS
(VDD = 10.8 V to 16.5 V; VSS = –5 V 6 10%; GND = 0 V; V
REF
= +2 V to +10 V1; RL = 2 k, CL = 100 pF unless otherwise
noted.) All specifications T
MIN
to T
MAX
unless otherwise noted.
5
Sample tested at 25°C to ensure compliance.
6
The glitch impulse transferred to the output of one converter (not addressed) due to a
change in the digital input code to another addressed converter.
Specifications subject to change without notice.
(VDD = +15 V 6 10%, VSS; = GND = 0 V; V
REF
= +10 V, RL = 2 k, CL = 100 pF unless otherwise noted.)
AII specifications T
MIN
to T
MAX
unless otherwise noted.
DUAL SUPPLY
BCTU
Parameter Version2Version Version Version Units Conditions/Comments
STATIC PERFORMANCE
Resolution 8 8 8 8 Bits Total Unadjusted Error
3
±2 ±1 ±2 ±1 LSB max VDD = +15 V ± 10%, V
REF
= +10 V Relative Accuracy ± 1 ± 1/2 ± 1 ±1/2 LSB max Differential Nonlinearity ± 1 ±1 ±1 ±1 LSB max Guaranteed Monotonic Full-Scale Error
4
± 1 ± 1/2 ± 1 ± 1/2 LSB max Typical tempco is 5 ppm/°C with V
REF
= +10 V Zero Code Error @ 25°C ±25 ±15 ±25 ±15 mV max Typical tempco is 30 µV/°C
T
MIN
to T
MAX
±30 ±20 ±30 ±20 mV max
Minimum Load Resistance 2 2 2 2 k min V
OUT
= +10 V
REFERENCE INPUT
Voltage Range
1
2 to 10 2 to 10 2 to 10 2 to 10 V min/V max Input Resistance 2 2 2 2 k min Input Capacitance
5
500 500 500 500 pF max Occurs when each DAC is loaded with all 1s. AC Feedthrough –70 –70 –70 –7 0 dB typ V
REF
= 8 V p-p Sine Wave @ 10 kHz
DIGITAL INPUTS
Input High Voltage, V
INH
2.4 2.4 2.4 2.4 V min
Input Low Voltage, V
INL
0.8 0.8 0.8 0.8 V max
Input Leakage Current ±1 ±1 ±1 ±1 µA max VIN = 0 V or V
DD
Input Capacitance
5
8 8 8 8 pF max Input Coding Binary Binary Binary Binary
DYNAMIC PERFORMANCE
5
Voltage Output Slew Rate 2 2 2 2 V/µs min Voltage Output Settling Time
Positive Full-Scale Change 5 5 5 5 µs max V
REF
= +10 V; Settling Time to ±1/2 LSB
Negative Full-Scale Change 5 5 5 5 µs max V
REF
= +10 V; Settling Time to ±1/2 LSB
Digital Feedthrough 50 50 50 50 nV secs typ Code transition all 0s to all 1s. V
REF
= 0 V; WR = V
DD
Digital Crosstalk
6
50 50 50 50 nV secs typ Code transition all 0s to all 1s. V
REF
= +10 V; WR = 0 V
POWER SUPPLIES
VDD Range 10.8/16.5 10.8/16.5 10.8/16.5 10.8/16.5 V min/V max For Specified Performance VSS Range –4.5/–5.5 –4.5/–5.5 –4.5/–5.5 –4.5/–5.5 V min/V max For Specified Performance I
DD
Outputs Unloaded; VIN = V
INL
or V
INH
@ 25°C 16 16 16 1 6 mA max T
MIN
to T
MAX
20 20 22 22 mA max I
SS
Outputs Unloaded; VIN = V
INL
or V
INH
@ 25°C 14 14 14 1 4 mA max T
MIN
to T
MAX
18 18 20 20 mA max
SINGLE SUPPLY
STATIC PERFORMANCE
Resolution 8 8 8 8 Bits Total Unadjusted Error
3
±2 ±1 ±2 ±1 LSB max Differential Nonlinearity ± 1 ±1 ±1 ±1 LSB max Guaranteed Monotonic Minimum Load Resistance 2 2 2 2 k min V
OUT
= +10 V
REFERENCE INPUT
Input Resistance 2 2 2 2 k min Input Capacitance
5
500 500 500 500 pF max Occurs when each DAC is loaded with all 1s.
DIGITAL INPUTS As per Dual Supply Specifications DYNAMIC PERFORMANCE
5
Voltage Output Slew Rate 2 2 2 2 V/µs min Voltage Output Settling Time
Positive Full-Scale Change 5 5 5 5 µs max Settling Time to ±1/2 LSB Negative Full-Scale Change 7 7 7 7 µs max Settling Time to ±1/2 LSB
Digital Feedthrough 50 50 50 50 nV secs typ Code transition all 0s to all 1s. V
REF
= 0 V; WR = V
DD
Digital Crosstalk
6
50 50 50 50 nV secs typ Code transition all 0s to all 1s. V
REF
= +10 V, WR = 0 V
POWER SUPPLIES
VDD Range 13.5/16.5 13.5/16.5 13.5/16.5 13.5/16.5 V min/V max For Specified Performance I
DD
Outputs Unloaded; VIN = V
INL
or V
INH
@ 25°C 16 16 16 1 6 mA max T
MIN
to T
MAX
20 20 22 22 mA max
NOTES
1
V
OUT
must be less than VDD by 3.5 V to ensure correct operation.
2
Temperature ranges are as follows:
B, C Versions; –40°C to +85°C T, U Versions; –55°C to +125°C
3
Total Unadjusted Error includes zero code error, relative accuracy and full-scale error.
4
Calculated after zero code error has been adjusted out.
SWITCHING CHARACTERISTICS
1, 2
Limit at 25°C Limit at T
MIN
, T
MAX
Limit at T
MIN
, T
MAX
Parameters All Grades (B, C Versions) (T, U Versions) Units Conditions/Comments
t
1
0 0 0 ns min Address to WR Setup Time
t
2
0 0 0 ns min Address to WR Hold Time
t
3
70 90 100 ns min Data Valid to WR Setup Time
t
4
10 10 10 ns min Data Valid to WR Hold Time
t
5
95 120 150 ns min Write Pulse Width
NOTES
1
Sample tested at 25°C to ensure compliance. All input rise and fall times measured from 10% to 90% of +5 V, tR = tF = 5 ns.
2
Timing measurement reference level is
V
INH+VINL
2
INTERFACE LOGIC INFORMATION
Address lines A0, A1 and A2 select which DAC accepts data from the input port. Table I shows the selection table for the eight DACs with Figure 1 showing the input control logic. When the
WR signal is low, the input latch of the selected DAC is transparent, and its output responds to activity on the data bus. The data is latched into the addressed DAC latch on the rising edge of
WR. While WR is high, the analog outputs remain at the value corresponding to the data held in their respective latches.
Table I. AD7228A Truth Table
AD7228A Control Inputs AD7228A WR A2 A1 A0 Operation
H X X X No Operation
Device Not Selected
LLLL DAC 1 Transparent
g
L L L DAC 1 Latched LLLH DAC 2 Transparent L L H L DAC 3 Transparent L L H H DAC 4 Transparent L H L L DAC 5 Transparent L H L H DAC 6 Transparent L H H L DAC 7 Transparent L H H H DAC 8 Transparent
H = High State L = Low State X = Don’t Care
+5 V SUPPLY OPERA TION
BCTU
Parameter Version Version Version Version Units Conditions/Comments
STATIC PERFORMANCE
Resolution 8888Bits Relative Accuracy ± 2 ±2 ±2 ±2 LSB max Differential Nonlinearity ±1 ±1 ±1 ±1 LSB max Guaranteed Monotonic Full-Scale Error ± 4 ±2 ±4 ±2 LSB max Zero Code Error
@ 25°C ±30 ±20 ± 30 ±20 mV max T
MIN
to T
MAX
±40 ± 30 ±40 ±30 mV max
REFERENCE INPUT
Reference Input Range 1.2 1.2 1.2 1.2 V min
1.3 1.3 1.3 1.3 V max Reference Input Resistance 2222k min Reference Input Capacitance 500 500 500 500 pF max
POWER REQUIREMENTS
Positive Supply Range 4.75/5.25 4.75/5.25 4.75/5.25 4.75/5.25 V min/V max For Specified Performance Positive Supply Current
@ 25°C 16161616µA max T
MIN
to T
MAX
20 20 22 22 µA max
Negative Supply Current
@ 25°C 14141414µA max T
MIN
to T
MAX
18 18 20 20 µA max
NOTES All of the specifications as per Dual Supply Specifications except for negative full-scale settling-time when V
SS
= 0 V.
Specifications subject to change without notice.
(VDD = +5 V 6 5%, VSS; = 0 to –5 V 6 10%, GND = 0 V, V
REF
= +1.25 V, RL = 2 kV, CL = 100 pF
unless otherwise noted.) AII specifications T
MIN
to T
MAX
unless otherwise noted.
(See Figures 1, 2; VDD = +5 V 6 5% or +10.8 V to +16.5 V; VSS = 0 V or –5 V 6 10%)
Figure 1. Input Control Logic
Figure 2. Write Cycle Timing Diagram
AD7228A
REV. A
–3–
AD7228A
REV. A
–4–
ABSOLUTE MAXIMUM RATINGS
1
VDD to GND . . . . . . . . . . . . . . . . . . . . . . . . . . .–0.3 V, +17 V
V
DD
to VSS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .–0.3 V, +24 V
Digital Input Voltage to GND . . . . . . . . . . . . . . . –0.3 V, V
DD
V
REF
to GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.3V, V
DD
V
OUT
to GND2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VSS, V
DD
Power Dissipation (Any Package) to +75°C . . . . . . . 1000 mW
Derates above 75°C by . . . . . . . . . . . . . . . . . . . . 2.0 mW/°C
Operating Temperature
Commercial . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C
Industrial . . . . . . . . . . . . . . . . . . . . . . . . . . –40°C to +85°C
Extended . . . . . . . . . . . . . . . . . . . . . . . . . –55°C to +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +150°C
Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . +300°C
NOTES
1
Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
2
Outputs may be shorted to any voltage in the range VSS to VDD provided that the power dissipation of the package is not exceeded. Typical short circuit current for a short to GND or VSS is 50 mA.
WARNING!
ESD SENSITIVE DEVICE
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the AD7228A features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality.
PIN CONFIGURATIONS
DIP AND SOIC PLCC
ORDERING GUIDE
Total
Temperature Unadjusted Package
Model
1
Range Error (LSB) Option
2
AD7228ABN –40°C to +85°C ±2 max N-24 AD7228ACN –40°C to +85°C ±1 max N-24 AD7228ABP –40°C to +85°C ±2 max P-28A AD7228ACP –40°C to +85°C ±1 max P-28A AD7228ABR –40°C to +85°C ±2 max R-24 AD7228ACR –40°C to +85°C ±1 max R-24 AD7228ABQ –40°C to +85°C ±2 max Q-24 AD7228ACQ –40°C to +85°C ±1 max Q-24 AD7228ATQ
3
–55°C to +125°C ±2 max Q-24
AD7228AUQ3–55°C to +125°C ±1 max Q-24
NOTES
1
To order MIL-STD-883, Class B processed parts, add /883B to part number.
Contact your local sales office for military data sheet and availability.
2
N = Plastic DIP; P = Plastic Leaded Chip Carrier (PLCC); Q = Cerdip;
R = Small Outline IC (SOIC).
3
These grades will be available to /883B processing only.
CIRCUIT INFORMATION D/A SECTION
The AD7228A contains eight identical, 8-bit, voltage-mode digital-to-analog converters. The output voltages from the con­verters have the same polarity as the reference voltage, allowing single supply operation. A novel DAC switch pair arrangement on the AD7228A allows a reference voltage range from +2 V to +10 V when operated from a V
DD
of +15 V. Each DAC consists of a highly stable, thin-film, R-2R ladder and eight high-speed NMOS switches. The simplified circuit diagram for one channel is shown in Figure 3. Note that V
REF
and GND are common to
all eight DACs.
Figure 3. D/A Simplified Circuit Diagram
The input impedance at the V
REF
pin of the AD7228A is the parallel combination of the eight individual DAC reference in­put impedances. It is code dependent and can vary from 2 k to infinity. The lowest input impedance occurs when all eight DACs are loaded with digital code 01010101. Therefore, it is important that the external reference source presents a low out­put impedance to the V
REF
terminal of the AD7228A under changing load conditions. Due to transient currents at the refer­ence input during digital code changes a 0.1 µF (or greater) decoupling capacitor is recommended on the V
REF
input for dc applications. The nodal capacitance at the reference terminal is also code dependent and typically varies from 120 pF to 350 pF.
Each V
OUT
pin can be considered as a digitally programmable
voltage source with an output voltage:
V
OUTN
= DN • V
REF
where DN is a fractional representation of the digital input code and can vary from 0 to 255/256.
The output impedance is that of the output buffer amplifier as described in the following section.
AD7228A
REV. A
–5–
OP AMP SECTION
Each voltage-mode D/A converter output is buffered by a unity gain noninverting CMOS amplifier. This buffer amplifier is tested with a 2 k and 100 pF load but will typically drive a 2 k and 500 pF load.
The AD7228A can be operated single or dual supply. Operating the part from single or dual supplies has no effect on the positive­going settling time. However, the negative-going settling time to voltages near 0 V in single supply will be slightly longer than the settling time for dual supply operation. Additionally, to ensure that the output voltage can go to 0 V in single supply, a transis­tor on the output acts as a passive pull-down as the output volt­age nears 0 V. As a result, the sink capability of the amplifier is reduced as the output voltage nears 0 V in single supply. In dual supply operation, the full sink capability of 400 µA at 25°C is maintained over the entire output voltage range. The single sup­ply output sink capability is shown in Figure 4. The negative V
SS
also gives improved output amplifier performance allowing an extended input reference voltage range and giving improved slew rate at the output.
Figure 4. Single Supply Sink Current
The output broadband noise from the amplifier is 300 µV peak-to-peak. Figure 5 shows a plot of noise spectral density versus frequency.
Figure 5. Noise Spectral Density vs. Frequency
DIGITAL INPUTS
The AD7228A digital inputs are compatible with either TTL or 5 V CMOS levels. All logic inputs are static-protected MOS gates with typical input currents of less than 1 nA. Internal in­put protection is achieved by on-chip distributed diodes.
SUPPLY CURRENT
The AD7228A has a maximum IDD specification of 22 mA and a maximum I
SS
of 20 mA over the –55°C to +125°C tempera­ture range. This maximum current specification is actually de­termined by the current at –55°C. Figure 6 shows a typical plot of power supply current versus temperature.
Figure 6. Power Supply Current vs. Temperature
APPLYING THIS AD7228A UNIPOLAR OUTPUT OPERATION
This is the basic mode of operation for each channel of the AD7228A, with the output voltage having the same positive po­larity as V
REF
. Connections for unipolar output operation are shown in Figure 7. The AD7228A can be operated from single or dual supplies as outlined earlier. The voltage at the reference input must never be negative with respect to GND. Failure to observe this precaution may cause parasitic transistor action and possible device destruction. The code table for unipolar output operation is shown in Table II.
Figure 7. Unipolar Output Circuit
AD7228A
REV. A
–6–
Table II. Unipolar Code Table
DAC Latch Contents MSB LSB Analog Output
1 1 1 1 1 1 1 1
+V
REF
255 256
 
 
1 0 0 0 0 0 0 1
+V
REF
129 256
 
 
1 0 0 0 0 0 0 0
+V
REF
128 256
 
 
=+
V
REF
2
0 1 1 1 1 1 1 1
+V
REF
127 256
 
 
0 0 0 0 0 0 0 1
+V
REF
1
256
 
 
0 0 0 0 0 0 0 0 0 V
Note: 1 LSB = (V
REF
)(2–8) = V
REF
1
256
 
 
BIPOLAR OUTPUT OPERATION
Each of the DACs on the AD7228A can be individually config­ured for bipolar output operation. This is possible using one ex­ternal amplifier and two resistors per channel. Figure 8 shows a circuit used to implement offset binary coding (bipolar opera­tion) with DAC1 of the AD7228A. In this case
V
OUT
= 1+
R2
R1
 
 
D
1•VREF
()
R2
R1
 
 
V
REF
()
With R1 = R2
V
OUT
= (2D1 – 1) • (V
REF
)
where D
1
is a fractional representation of the digital word in
latch 1 of the AD7228A. (0 D
1
255/256)
Figure 8. Bipolar Output Circuit
Table III. Bipolar Code Table
DAC Latch Contents MSB LSB Analog Output
1 1 1 1 1 1 1 1
+V
REF
127 128
 
 
1 0 0 0 0 0 0 1
+V
REF
1
128
 
 
1 0 0 0 0 0 0 0 0 V 0 1 1 1 1 1 1 1
–V
REF
1
128
 
 
0 0 0 0 0 0 0 1
–V
REF
127 128
 
 
0 0 0 0 0 0 0 0
–V
REF
128 128
 
 
= –V
REF
Mismatch between R1 and R2 causes gain and offset errors, and therefore, these resistors must match and track over temperature.
Once again, the AD7228A can be operated from single supply or from dual supplies. Table III shows the digital code versus output voltage relationship for the circuit of Figure 8 with R1 = R2.
AC REFERENCE SIGNAL
In some applications it may be desirable to have an ac signal ap­plied as the reference input to the AD7228A. The AD7228A has multiplying capability within the upper (+10 V) and lower (+2 V) limits of reference voltage when operated with dual sup­plies. Therefore, ac signals need to be ac coupled and biased up before being applied to the reference input. Figure 9 shows a sine-wave signal applied to the reference input of the AD7228A. For input frequencies up to 50 kHz, the output distortion typi­cally remains less than 0.1%. The typical 3 dB bandwidth for small signal inputs is 800 kHz.
Figure 9. Applying a AC Signal to the AD7228A
TIMING DESKEW
A common problem in ATE applications is the slowing or “rounding-off” of signal edges by the time they reach the pin-driver circuitry. This problem can easily be overcome by “squaring-up” the edge at the pin-driver. However, since each edge will not have been “rounded-off” by the same extent, this “squaring-up” could lead to incorrect timing relationship be­tween signals. This effect is shown in Figure 10a.
Figure 10a. Time Skewing Due to Slowing of Edges
The circuit of Figure 10b shows how two DACs of the AD7228A can help in overcoming this problem. The same two signals are applied to this circuit as were applied in Figure 10b. The output of each DAC is applied to one input of a high-speed comparator, and the signals are applied to the other inputs. Varying the output voltage of the DAC effectively varies the trigger point at which the comparator flips. Thus the timing re­lationship between the two signals can be programmably cor­rected (or deskewed) by varying the code to the DAC of the AD7228A. In a typical application, the code is loaded to the
AD7228A
REV. A
–7–
DACs for correct timing relationships during the calibration cycle of the instrument.
Figure 10b. AD7228A Timing Deskew Circuit
COARSE/FINE ADJUST
The DACs on the AD7228A can be paired together to form a coarse/fine adjust function as indicated in Figure 11. The func­tion is achieved using one external op amp and a few resistors per pair of DACs.
DAC1 is the most significant or coarse DAC. Data is first loaded to this DAC to coarsely set the output voltage. DAC2 is then used to fine tune this output voltage. Varying the ratio of R1 to R2 varies the relative effect of the coarse and fine DACs on the output voltage. For the resistor values shown, DAC2 has a resolution of 150 µV in a 10 V output range. Since each DAC on the AD7228A is guaranteed monotonic, the coarse adjust­ment and fine adjustment are each monotonic. One application for this is as a set-point controller (see “Circuit Applications of the AD7226 Quad CMOS DAC” available from Analog Devices, Publication Number E873–15–11/84).
Figure 11. Coarse/Fine Adjust Circuit
SELF-PROGRAMMABLE REFERENCE
The circuit of Figure 12 shows how one DAC of the AD7228, in this case DAC1, may be used in a feedback configuration to provide a programmable reference for itself and the other seven converters. The relationship of V
REF
to VIN is expressed by
V
REF
=
1+G
()
1+GD
1
()
V
IN
where G = R2/R1
Figure 13 shows typical plots of V
REF
versus digital code, D1, for
three different values of G. With V
IN
= 2.5 V and G = 3 the voltage at the output varies between 2.5 V and 10 V giving an effective 10-bit dynamic range to the other seven converters. For correct operation of the circuit, V
SS
should be –5 V and R1
greater than 6.8 k.
Figure 12. Self-Programmable Reference
Figure 13. Variation of V
REF
with Feedback Configuration
MICROPROCESSOR INTERFACING
Figure 14. AD7228A to 8085A/Z80 Interface
Figure 15. AD7228A to 6809/6502 Interface
AD7228A
REV. A
–8–
C1663–24–5/92
PRINTED IN U.S.A.
Figure 16. AD7228A to 68008 Interface
Plastic DIP (N-24)
SOIC (R-24)
Cerdip (Q-24)
PLCC (P-28A)
Figure 17. AD7228A to MCS-51 Interface
OUTLINE DIMENSIONS
Dimensions shown in inches and (mm).
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